This invention relates to the preparation of finely divided free flowing polymeric particles made from normally tacky plastic materials such as amorphous polyolefins and adhesives based thereon.
Polymeric materials are produced, sold and handled in many different forms. However, the particulate form of these polymeric materials is generally a more preferred form. Generally the particulate form of polymeric material is easily produced at high rates and is preferred by most users due to ease in handling, shipping and processability. Therefore, it is generally desirable when producing polymer materials to end up with a commodity or form of material that is widely accepted in the industry such as particles or pellets. These particles or pellets are generally produced by extruding the polymer material in molten state through a die followed by cutting. Sometimes the die is immersed in water to solidify the pellets more quickly, such as in an underwater pelletizer.
Certain polymeric materials produce particles or pellets that are inherently tacky and the recovery from the manufacturing process in the form of usable pellets is extremely difficult. One method of reducing the tackiness of these particles is to coat them with a small amount of a non-sticky material, such as a powdered solid. Several different methods of coating these particles with the powdered material have been developed. One method is to simply mix the formed polymer particles with the powder by agitation, e.g. tumbling, airveying, etc. A more sophisticated process is strand pelletizing, in which the material is extruded into strands that are then dusted with the non-sticky powdered solid followed by cutting the strands into pellets.
It has been found that certain polymeric compounds that are inherently "soft and tacky" such as certain amorphous polyolefins and adhesives based thereon are extremely difficult to process into the form of usable pellets by conventional pelletization methods. These materials generally have a low degree of crystallinity and solidify slowly. These materials will either gum up or smear on the rotary knives of a pelletizer, plug the conveying lines, or block after being stored for a short period of time, particularly at elevated temperatures, and are not free flowing. These materials must then be produced and sold in some other less desirable form, such as large solid blocks or powder coated slats. It would, therefore, be desirable if a process could be developed to produce free flowing particles of these soft and tacky materials.